Recent microbiological studies have suggested the existence of a periodontal disease-associated microflora which involves elevated proportions of certain organisms in the indigenous microbiota. The proposed study will use the ligature-induced periodontitis model in monkeys to monitor shifts in the subgingival flora during the transition from gingivitis to periodontitis. Antibacterials will be used to selectively alter plaque levels of certain microorganisms to evaluate their role in the disease process. This approach should determine if predictable changes in the subgingival flora precede disease and if specific organisms are essential to the process. Proven quantitative anaerobic culturing procedures will be used for the monitoring of 11 key bacteria and the identification of other predominant organisms. Preliminary data demonstrate the subgingival flora of the monkey is comparable to the flora associated with gingivitis in man and may be shifted by means of ligatures to a flora comparable to one associated with periodontitis in humans.